Chemical manufacture



.duced: and also unreacted pyridine, =steam,;is subjectedtoa separation whereby 2-chloropyri- ,dineisremovede The residue from this .separation is .treatedtorecover therefrom an azeotropic mixture of .steamand pyridine (ie. steamand pyridine in the proportion-of..about 4 United tates PatentO ice out the use of any reactor packing and also with glassbeads as reactor packing. However, better yields have been obtained with the use as reactor packing of a porous, granular material providing a large surface per unit volume, such as alumina, activated carbon; and silicon carbide. To date the best results have been obtained'with silicon carbide.

The reactor efiluent'contains Z-chIoropyridine, chlorine, hydrogenchloride,pyridineiand steam. In order to separate 2-chloropyridine from this mixture, the 2-chloropyridine and pyridine can be absorbed in an aqueous abthesedifiiculties, the'reaction has also been. carried out withv the reactants in admixture with nitrogen. This procedurersuifers from thedisadvantages, however, that relatively pure nitrogen is uneconomical to use and that the's-yield of 2-chloropyridine is undesirablylow based entire amount of pyridine consumed;

In accordance with the present inventiongit has been discovered thatZ-chloropyridine can be conveniently preparedin good yield by conducting the vapor phase'reactionof chlorine and pyridine in the presence. of steam.

The use of steam is advantageous as it is inexpensive and is readily available. Moreover, the use of steam simplifies the manufacture because it permits the recovery of-pyridine as the pyridine-water azeotrope which can be conveniently recycled through .the process. Thus,

the invention provides-an economical method for the manufacture of 2-chloropyridine.

Accordingly; the method of the'present invention come prises carrying out'the vapor phase reaction of chlorine and pyridine with these reactants in admixture with steam. At least about 0.25-mole of steam,-and" preferably from about 0.5 to 2.0 moles'of steam, are introduced into the reaction zone per mole of pyridine. I have found that the use of 1 mole of' steam 'permole of pyridine is very satisfactory and moderates the reaction so that good temperature control can be'maintained. There 1 appears to be noupper limit to the amount of steam that can be used other than that imposed by the-expense of handling a large amount of material.

The initial relative proportion of the reactants chlorine and pyridine can be varied widely, for. example from 0.5

or:1ess'to 1.5 or more moles of chlorine 'per mole of pyridine. The reactioncan be carried out: at' atemperature.of 260lto 380 C., and preferably at 325 to 355 C.

,In a preferred embodiment of the invention, unreacted pyridine isrecovered as a steam-pyridine azeotropic mixture,;and.this mixture is recycled through the process. In this embodiment, the efiiuent from the reactor, which contains theZ-chloropyridine and the hydrogen. chloride prochlorine .and the moles .of steam. per. mole. of: pyridine) This azeotropicmixtureis then used as. at least part .of the pyridine and steam introduced into the reactor;

The reactionoi chlorineand pyridine according to the invention canhecarriedoutin a glass reactor containing aporous bed of silicon carbide and provided with means desired reaction temperature-within 'the reactorw Thereactants and the steam, preferably preheated to about-reaction temperature, are advantageously introduced into the reactor at a rate corresponding to a residence time in the reaction-zone of from 1 to '5 seconds.

The method of the invention has been carried out withsorbent and the. resulting solution can then be treated to render theZ-chloropyri'dirie amenable to separation by extraction. Following extraction, the .Z-chloropyridine can be purified by distillation.

To separate '2-chloropyridine from the reactor efiiuent inthis manner, the reactor effiuent is scrubbed with a dilute solution of a halogen acid, for example, hydrochloric acid. When so treated with a halogen acid, the 2- chloropyridine and theunreacted pyridine are absorbed andgointo solution asJ-chloropyridine hydrohalide and pyridine ,hydrohalide. Anaqueousalkaline solution, for examplea sodium. hydroxide solution, is added to the solution. of thehydrohalides in an amount suflicient to liberate v2-chloropyridine as free base, but insufficient to liberate pyridine as free :base. 2-chloropyridine is then separated by extraction withether, 2-chloropyridine dissolving inthe ether phase. Following extraction, ether is evaporated-from theQ-chloropyridine, and the Z-chloropyridine is then.purified by distillation.

Thecresidue from the ether extraction is an aqueous phase=containing pyridine hydrochloride. This residue can be treated.tobbtaintherefrom a pyridine-steam azeo: tropic mixture which can=be used as atleast partofthe pyridine andsteam-fedto the reactor. wherein 2-chloro-. pyridine is formed. T 0 do this the extraction residueis first treated with an aqueous a kalinesolution, for ex ample anaqueous sodium hydroxide solution, toliberate asfree base pyridine from the pyridinehydrohalide. The resulting pyridine solution is thensubjectedto distillation torecover therefrom the azeotropic-mixturev of pyridine and steam. This mixture-is then recycledthrough the reactor.-

If desired, 2-chloropyridine can be separated fromthe 2-chloropyridine free base-pyridine hydrochloridesolution .by subjecting. this solution to steam distillation. Upon distillation,. 2-chloropyridine is collected as the overhead product. A pyridine-steamazeotropic mixture can be obtained from the resulting distillation residue by treating this residuein'the same way in'which the residue ofthe abovevdescribed ether extraction was treated.

In anothermodificationofthe method of the invention, 2-chloropyridine can berecovered from the. solution of2- chloropyridine hydrohalide and pyridine hydrohalide by treating this solution with an aqueous alkaline solution sufficientinbamountatovraise the pH to 10-1-1 and thereby liberate both-2rchloropyridine and pyridine as free-bases, separatingithese freebases from theirsolvent by extraction with ether: and then-separating this ether phaseintoether, pyridineandZ-thloropyridine by distillation.

The: following examples describe specific embodiments of the invention.

Example 1 the level ofthe entrance end andwasheated during: the

courseofthe reaction by an electric tube furnace. -The "reaction "temperature was measured by: a thermocouple placed in a thermowell sealed into the reactor wall and reaching into the center of the reaction zone.

A pyridine and water mixture formed of 2.36 moles pyridine and 2.36 moles of water was pumped with a Micro bellows pump set to deliver at a pre-determined rate from a graduated addition funnel into an electrically heated vaporizer and pro-heater. The vapor mixture was heated to 345-355 C. (reaction temperature) and was then conducted to a point along the axis of the reaction tube just short of the packed section and there released into the reactor. At the same time, 2.1 moles chlorine gas was metered from a cylinder-by means of a needle valve and rotameter. and was heated to 345-355 C. The chlorine gas was then conducted into the reactor and released at a point in the reactor short of the point where the pyridine-water mixture was released. Thus some mixing of the reactants occurred before the reactants came in contact with the reactor packing.

During the reaction, the reaction temperature was maintained at 345-355 C. The total reaction time was hours, 37 minutes. The average residence time of the gases in the portion of the reactor packed with silicon carbide was 3.5 seconds.

The reactor effluent was quenched and scrubbed with cold aqueous hydrochloric acid by countercurrent contacting in a glass column packed with glass beads. In the course of this scrubbing, 2-chloropyridine and pyriout. In general more 2,6-dichloropyridine is produced at reaction temperatures in the upper part of the range of 260 to 380 C., and more 3-chloropyridine is produced at reaction temperatures in the lower part of this range. As stated hereinbefore, the preferred range for the production of 2-chloropyridine is 325 to 355 C. Z-chloropyridine can be used as a fungicide as .isdis closed by Schefier and Duncan, Industrial and Engineering Chemistry 38, 619-21 (1946).

I claim: a

l. A method of making 2-chloropyridine which comprises reacting chlorine and pyridine in vapor phase and a in admixture with steam, at least about 0.25 mole of steam being introduced into the reaction zone per mole of pyridine.

2. A method of making 2-chloropyridine which'comprises'reacting chlorine and pyridine in vapor phase and in admixture with steam at a temperature of 260t'o 380' dine was absorbed in the hydrochloric acid solutionand formed therein 2-chloropyridine hydrochloride and pyridine hydrochloride. The solution of the hydrochlorides was adjusted to a pH of 3 by the addition thereto of aqueous sodium hydroxide. At this pH, chloropyridine exists primarily as the free base while pyridine is in the form of its hydrochloride. The chloropyridine, pyridine-hydrochloride solution was then subjected to an extraction operation in which ether was mixed with the solution and chloropyridine dissolved in the ether phase. The ether was then evaporated from the ether, 2-chloropyridine solution and the 2-chloropyridine was then purified by distillation.

The residue from the ether extraction which contains pyridine hydrochloride was adjusted to pH 10 to 11 by addition thereto of aqueous sodium hydroxide. At this pH pyridine exists mainly as the free base. The resulting pyridine solution was then subjected to distillation and the water-pyridine azeotrope was removed as a gas. This azeotropic mixture can be used as reactor.

The purified 2-chloropyridine boiled at 83-84 C.. at 42-43 mm. of Hg and had an index of refraction n =1.53O8. The literaturevalue for these constants are B. P. at 15 mm. of Hg, 62.63 C., and n =1.5322. The yield of 2-chloropyridine was 93.9 g. or 38 percent of theory. 31 percent of the pyridine was recovered unchanged. The yield of 2-chloropyridine based on pyridine consumed was 55 percent. Some 2,6-dichloropyridine was also isolated in this example.

Example 2 In this "example the equipment described in Example 1 was used. 1.18 moles of pyridine, 1.18 moles of steam and 0.94 mole of chlorine were reacted at 345-355 C. over a period of 2 hours and minutes. The residence time in the silicon carbide bed was 3.1 seconds. The crude 2-chloropyridine' fraction isolated by distillation of the reactor eifiuent boiled at 166-l76 C. at '1 atmosphere (literature value at 1 atmosphere, 170 C.) and had an index of refraction n :1.5319. This product contained some dichloropyridine but amounted to a 48 percent pass yield of crude'Z chIoropyridine. 35.5 grams of pyridine was recovered. 1 The yield of crude 2-ch1oropyridine based on pyridine consumed was 77 percent.

The amount of chloropyridines other, than 2-chloropyridine produced by the method of the invention depends on the" conditions under whichthereaction is carried largely part of the feed to the C., the initial relative proportion of the reactantsbeing about 0.5 to about 1.5 moles of chlorine per mole of pyridine and the-initial relative proportion of steam to pyridine being from 0.5 to 2.0 moles of steam'perrmole of pyridine. I I

-3. A method of making 2-chloropyridine which comprises reacting chlorine and pyridine in the vapor phase and in admixture with steam and in the presen'ceof silicon carbide at a temperatureof 260 to 380 C., the initial relative proportion of the reactants being about'0.5 to about 1.5 moles of chlorine per mole of pyridine and the initial relative proportion of steam to. pyridine being from 0.5 to 2.0 moles of steam per mole of pyridine.

4. A method of making 2-chloropyridine by reacting chlorine and pyridine'in the vapor phase, said; method comprising introducing into a reactor said reactants and steam, the initial relative proportion of the reactants be the azeotropic mixture thereof, and using said azeotropic mixture as at least part of the pyridine and steam introduced into said reactor.

5. A method of making 2-chlor0pyridine by reacting.

chlorine and pyridine in the vapor phase, said method comprising introducing into a reactor said reactants and steam, the initial relative proportion of the, reactants being 0.5 to 1.5 moles of chlorine to 1 mole of pyridine and the initial relative proportion of steam to pyridine about 0.5 to 2.0 moles of steam to 1 mole of pyridine, maintaining the temperature within the reactor at 325 to 355 C., contacting the reactor eflluent with an aqueous hydrochloric acid solution whereby unreacted pyri-' dine and 2-chloropyridine formed during the reaction are absorbed by said solution and form therein a solution of pyridine hydrochloride and 2-chloropyridine hydrochloride, adding to the solution of hydrochlorides aqueous sodium hydroxide in amount suflicient to vliberate as free base only 2-chloropyridine, separating liberated 2-chloropyridine from the 2-chloropyridine-pyridine hydrochloride solution and recovering from the resulting residue pyridine and steam as the azeotropic mixture thereof, and using said azeotropic mixture as at least part of the pyridine and steam introduced into said reactor.

References Cited in the file of this patent UNITED STATES PATENTS Prahl June 19, 1934 Wibaut et a1 Oct. 23,1934

OTHER REFERENCES 7 Wibaut et al.: Rec. trav cbim., vol 58, pp., 709 .-2 1 

1. A METHOD OF MAKING 2-CHLOROPYRIDINE WHICH COMPRISES REACTING CHLORINE AND PYRIDIEN IN VAPOR PHASE AND IN ADMIXTURE WITH STEAM, AT LEAST ABOUT 0.25 MOLE OF STEAM BEING INTRODUCTED INTO THE REACTION ZONE PER MOLE OF PYRIDINE. 